LINKED LOWSTAND DELTA TO BASIN-FLOOR FAN DEPOSITION, OFFSHORE EAST KALIMANTAN: AN ANALOGUE FOR DEEP-WATER RESERVOIR SYSTEMS

摘要

In the offshore East Kalimantan, 3D seismic reflectors can be traced downslope from a Pleistocene lowstand delta to the basin-floor fan, giving insight into the distribution of sands in ancient deep-water settings. The cycles on the shelf were dominated by progradational packages deposited during highstands and falling eustatic sea level. During the last two lowstands of the sea level (～18 and ～130 ka), coarse elastics were not deposited in deep-water environment because existing growth faults and regional subsidence prevented lowstand deltas from reaching the slope. During the lowstand of sea level that ended at ～240 ka, a delta prograded over the previous shelf edge, and sand-rich sediments spilled onto the slope. A canyon on the slope connected the 240 ka lowstand delta to a coeval basin-floor fan. The canyon has a sinuous fill that consists of a lower, amalgamated channel complex and an upper channel-levee complex. The basin-floor fan at the toe of the slope can be differentiated < into two parts. The stratigraphically lower part of the basin-floor fan has broad lobes with relatively continuous reflectors. The stratigraphically higher part has a sinuous channel-levee complex that prograded over the lower fan and feed the lobes at the outermost fan. The amalgamated channel fills on the slope and sheet-like lobes on the basin-floor fan have moderate- to high-amplitude reflectors and are inferred to represent sand-rich, early lowstand deposits. The channel-levee complexes on the slope and basin floor are dominated by low-amplitude reflectors and are inferred to be mud-rich strata deposited during the late lowstand. Unlike the classic sequence stratigraphy models,rnthese lowstand strata do not onlap to the slope; rather, deep-water elastics extend from the last clinoforms of lowstand deltas. In this system, lowstand deltas determined when and where sand-rich sediments entered pre-existing canyons on the slope to feed basin-floor fans.